The present invention generally relates to a synchronizing signal generator for a PAL television signal processing system, and is directed more particularly to a synchronizing signal generator to enable a color television camera to encode a video signal according to the PAL television system.
In the color television signal of the PAL system, the following relationships exist among the color sub-carrier frequency f.sub.SC, the horizontal synchronizing frequency f.sub.H and the vertical synchronizing frequency f.sub.V : ##EQU1##
The above relationships are established so that, when the color sub-carrier signal component is mixed with the luminance signal and dark and bright dots are produced on a television picture tube, these dots are not conspicuous to a viewer.
If a reference oscillator with an oscillation frequency the same as the frequency f.sub.SC of the color sub-carrier is provided and the oscillation output therefrom is frequency divided, synchronizing frequency signals having the relationship (2) cannot be produced. More particularly, it is necessary that a signal whose frequency is lower than that of the color sub-carrier frequency f.sub.SC by 1/2f.sub.V (=25 Hz) be provided and then frequency divided. Due to this non-integral relationship, such a synchronizing signal forming circuit cannot be provided by a digital circuit alone since digital frequency division is limited to division by an integer. It is theoretically possible to use a reference oscillator, whose oscillation frequency is equal to the color sub-carrier frequency f.sub.SC times the least common multiple of the denominators in equation (1). With such a reference oscillator frequency, both the color sub-carrier signal f.sub.SC and the horizontal and vertical synchronizing frequency signals can be provided by merely frequency dividing the output from the reference oscillator. However, this requires that the reference oscillator generate a frequency of about 11 GH.sub.z. Such a high frequency reference oscillator is not practical at the present time.